Stroboscopic light valve checking machine



Match 9, 1948. J, P, @RCORAN 2,437,419

STROBOSCOPIC LIGHT VALVE CHECKING MACHINE Filed July 12, 1944 Pig 4 /NV TOR JAMES P. CORCORAN ATTORNEY Patented Mar. 9, 1948 James "Patrick Corcoran, West Los Angeles, Calii., assignor to Twentieth Century-Fox Film Corporation, Los Angeles, .Calif., a corporation of New York Application July 12, 1944, Serial No. 544,525 Claims. (01. 88-14) This invention relates to the art of electrooptically photographing sound and deals particularly with a machine for checking light valves used in a certain method in the above art.

The invention to be described hereinafter is directed to those versed in the art of sound recording. To these it is well known that one method of recording sound employs a light valve.

There are several types of valves used 'for this.

purpose. The most common type employs two spaced parallel ribbons strung in a magnetic field so that alternating current conducted by the ribbons will cause them to vibrate proportionally and in accordance wlth the electrical impulses of the current. However, it should be stated that there are other types of valves employing more than two ribbons. For instance, there is a double section valve employing four ribbons which is used for push-pull recording. The invention to be described and illustrated herein is adapted to check both types of valves, as will appear to those skilled in this art.

In using light valves, there are several critical factors. The spacing of the two ribbons. must be accurate, and accordingly is done with a microscope. The resonance of the ribbons must likewise fall within a certain prescribed range of frequencies. The tension on the two' ribbons must be precisely equal so that the two ribbons will resonate with substantially the same amplitude and frequency. Heretofore, all these factors have been known and'the ribbons have been strung according to precalculated figures. But it required a combination ofmechanical, electrical, optical, and photographic devices and apparatuses to check the above factors before the valves were allowed to go into production.

My invention provides a means whereby the light valve of either the two-ribbon or four-ribbon type may be viewed while operating under normal working conditions. the light slit produced by the valve is scanned by an apertured disk rotating in synchronism with the oscillation of the valve strings to produce standing waves that are projected onto a translucent screen to show the ribbons in all positions of their swing. In this way, the various above mentioned characteristics of the valve may be visually examined and analyzed without recourse to the usual means heretofore used for this purpose.

Accordingly, it becomes the primary object of my invention to provide .a means whereby light valves, either of the two-ribbon or four-ribbon type, may be visuallyHanalyzed under working At the same time,

2 conditions to determine certain characteristics of the valve.

Another object is to provide a light valve checking machine having a light slit scanning member wherein the valve oscillations and the rate at which the slit is scanned are synchronously related.

Other objects and advantages will become apparent as the description proceeds in conjunction with the drawing, in which:

Figure 1 is a more or less diagrammatic view of my machine;

Figure 2 is a fragmentary view taken on line 2--2 of Figure -1;

Figure 3 is an illustration of the viewing screen as it would appear with a two-ribbon valve shown under working conditions;

Figure 4 .is a view of the same screen showing the same valve as it would appear at rest; and

Figure'5 is a fragmentary perspective view of a two-ribbon valve showing the fundamental arrangement of parts for such a valve.

Briefly stated, my invention amounts to a machine whereby the image of the slit between the ribbons of a light valve may be projected upon a translucent screen. The optical system for this purpose will be described later. In conjunction with the means for projecting the image of the slit, I provide a means for modulating the ribbons and another means for scanning the slit on the .screenin synchronism with the modulation of the ribbons. The resultof the scanning device workingin synchronism with the modulation of the ribbons is a fixed standing wave on the screen which shows the nodes and loops of the oscillating ribbons. This image being projected .on a translucent screen may be seen by the naked eye, thus disclosing valuable information as to what is actually taking place in the operation of the valve;

Referring to Figure 1, wherein I have shown diagrammatically a complete set-up for practicing my invention, it will be seen that this view, generally speaking, includes a suitable case H. Mounted within the case ll are the various component parts of my machine which in general comprise a. motor ii, a scanning disk I3 adapted to be operated by the motor, a viewing screen [4 arranged in iront of the scanning disk, a light valve l5, and a light l6 adapted to throw light on to the valve.

Referring to Figure 5, wherein I have shown the elements of valve I5 fragmentarily, it will be seen that this valve comprises ribbons I! and I8 strung in parallelism between pole pieces [9.-

This is known as the two-ribbon valve. A fourribbon valve for a push-pull set-up would comprise two of these units spaced substantially end in one direction through the valve. The biasing current is supplied by the battery 13 and flows through conductor 20 to the ribbons l1 and i8 and then through conductors 2| and 22 to a transformer T which is mid-tapped to the opposite side of battery B through a switch S. The same battery B supplies current to the lamp l6 through conductors 23, 24, and switch 25. Modulation is supplied to the valve through the transformer T and conductors 2| and 22, said transformer being energized by conductors 26 and 2'1 that connect an alternating current generator section G, or its equivalent, driven by the motor l2 to the transformer T. A switch 28 may be inserted in this circuit if desired.

In conjunction with the above, I provide an optical system consisting of a lens assembly 29, a prism 30, a cylindrical lens 3|, and a tiltable mirror 32 arranged to project an image of the valve slit onto the screen 14. The mirror 32 is mounted on a shaft 32 so that an image of the slit may be projected on line 33 or 34 as desired, by rotating the shaft slightly in one direction or the other. The cylindrical lens 3| is arranged to cover the full length of the light slit image and is for the purpose of magnifying the width of the slit while holding the length fixed. The foregoing may be suitably mounted on the housing H.

The disk [3 is arranged to rotate in the plane of and close to the screen l4 and is formed with radial slots 35 seen in Figure 2. As before stated, the mirror 32 is arranged to be tilted so that an image of the slit can be projected on a line 33 or 34 as desired. When projected on the line 33, the image falls below the circumference of the disk l3 and appears as a straight line slit 36, as shown in Figure 4. When projected on the line 34, the image of the slit appears as shown by the dotted lines 3'! in Figure 2. In this position, the slit is scanned by rotating the disk 13. The scanning result ,is produced by the action of a vertical slit sweeping across an expanding and contractin light slit, combined with the retentive power of the eye.

It is to be understood that upon rotating the disk l3 the generator section G of the motor I2 generates a frequency which is in synchronism with the number of slits passing by a certain point per second. In other words, the number of poles in the generator G is proportional to the number of slits in the disk l3. In this way it is impossible for the modulation of the valve and the scanning of the valve slit to ever get out of synchronism. When the slit is projected on line 34 and is scanned by the disk [3, the result is an image 38 of a standing wave. (See Fig. 3.) An image of this nature may be visually studied and analyzed. It discloses the amplitude of the signal and whether or not the ribbons are clashing. It also shows if there is any bowing between the two ribbons.

In the view shown in Figure 4, wherein the ribbons are stationary, the actual spacing of the ribbons may be checked and the amount of bias required to bring the ribbons to a certain predetermined spacing may also be checked. Other and varied uses of the device will occur to those skilled in this art.

Although I have shown my machine in conjunction with a two-ribbon valve, nevertheless it is to be understood that its usefulness extends to the four-ribbon valve, where it may be employed to a definite advantage in balancing the two sections of the valve against each other, in addition to the other advantages and uses mentioned hereinbefore.

I claim:

1. In a machine for checking light valves having vibratory ribbons with a light slit therebetween, means for projecting an image of said light valve slit onto a viewing screen, means for vibrating the ribbons of said valve, and means for stroboscopically scanning said image lengthwise of said slit in timed relation to the vibrations of said ribbons.

2. In amachine for checking light valves having vibratory ribbons with a light slit therebetween, optical means for projecting an image of said light valve slit onto a viewing screen, electrical means for vibrating the ribbons of said valve to vary the width of said light slit at a predetermined frequency, and scanning means synchronously related with said electrical means for stroboscopically scanning said image lengthwise of said slit.

3. In a machine for checking light valves having vibratory ribbons with a light slit therebetween, means for mounting said valve in said machine, a light source for illuminating said light slit, optical means for projecting an image of said slit onto a viewing screen, means for vibrating the ribbons of said valve to vary the width of said slit, and scanning means synchronously related with said means for vibrating said ribbons for stroboscopically scanning said image lengthwise of said slit.

4. In a machine for checking light valves having vibratory rib-bons with a light slit therebetween, a viewing screen, means for projecting an image of said light valve slit onto said screen, a motor in said machine, a generator driven by said motor, adapted to supply current for vibrating the ribbons of said valve, and a scanning disk driven by said motor having apertures radially disposed therein adapted to scan said image lengthwise of said slit at a frequency in synchronism with the frequency of vibration of said ribbons said frequency bein at a rate sufficient to maintain persistence of vision.

5. In a machine for checking light valves having vibratory ribbons with a light slit therebetween, means for mounting said valve in said machine, means for vibrating the ribbons of said valve to vary the width of the light slit in said valve, means for projecting an image of said vibrating light slit onto a viewing screen, and means for stroboscopically scanning said image lengthwise of said slit at a frequency in timed relation to the frequency of vibration of said ribbons said frequency being at a rate suiiicient to maintain persistence of vision.

6. In a machine for checking light valves having vibratory ribbon-s with a light slit therebetween, optical means for projecting an image of said light valve slit onto a viewing screen, electrical means for vibrating the ribbons of said valve to vary the width of said light slit at a predetermined frequency, and scanning means synchronously related with said electrical means for stroboscopically scanning said, image lengthwise of said slit, said optical means having a tiltable, light-reflecting member for moving said image into and out of the field of operation of said scanning means.

7. In a machine for checking light valves having vibratory ribbons with a light slit therebetween, means for projecting an image of said light valve slit onto a viewing screen, means adapted to electrically energize the ribbons of said valve to vibrate the same, means adapted to stroboscopically scan said image lengthwise of said slit, and a motor arranged to actuate said last two mentioned means in synchronous relation with each other.

8. In a machine for checking light valves having vibratory ribbons with a light slit therebetween, means for projecting an image of said light slit onto a viewing screen, said means including a cylindrical lens arranged to cover said image and magnify the width of the same while holding the length fixed, means for vibrating the ribbons of said valve to vary the width of said slit, and means for stro boscopically scanning said image lengthwise of said slit in timed relation to the vibration of said ribbons.

9. In a machine for checking light valves having vibratory ribbons with a light slit therebetween, optical means for projecting the image of said ribbons onto a screen, means for vibrating said ribbons to vary the width of said light slit at a predetermined frequency, and scanning means synchronously related to said vibrating means for stroboscopically scanning said image lengthwise of said slit, said scanning means and said vibrating means including a motor, a generator driven by said motor, means for supplying current from said generator to said vibrating means to vibrate said ribbons, a rotatable disk driven by said motor having radially disposed slotted apertures therein arranged to scan said image lengthwise of said slit and pass intermittent light at a rate sufiicient to maintain persistence of vision of said image.

10. In a machine for checking light valves having vibratory ribbons with a light slit therebetween, means for projecting an image of said light valve slit onto a viewing screen, a motor arranged to drive a means for vibrating the ribbons of said valve, means driven by said motor for stroboscopioally scanning said image length wise of said slit in timed relation to the vibration of said ribbons to produce a visible standing image of said light valve slit.

' JAMES PATRICK CORCORAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

